/*
 * The contents of this web application are subject to the Mozilla Public License Version 
 * 1.1 (the "License"); you may not use this web application except in compliance with 
 * the License. You may obtain a copy of the License at http://www.mozilla.org/MPL/.
 * 
 * Software distributed under the License is distributed on an "AS IS" basis, 
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License 
 * for the specific language governing rights and limitations under the License.
 * 
 * The Original Code is owned by and the Initial Developer of the Original Code is 
 * Composite A/S (Danish business reg.no. 21744409). All Rights Reserved
 * 
 * Section 11 of the License is EXPRESSLY amended to include a provision stating 
 * that any dispute, including but not limited to disputes related to the enforcement 
 * of the License, to which Composite A/S as owner of the Original Code, as Initial 
 * Developer or in any other role, becomes a part to shall be governed by Danish law 
 * and be initiated before the Copenhagen City Court ("K�benhavns Byret")            
 */

using System;
using System.Threading;
using System.Threading.Tasks;

namespace Composite.Core.Parallelization
{
    internal sealed class AsyncLock
    {
        private readonly SemaphoreSlim _semaphore = new SemaphoreSlim(1, 1);
        private readonly Task<IDisposable> _releaser;

        public AsyncLock()
        {
            _releaser = Task.FromResult((IDisposable)new Releaser(this));
        }

        public Task<IDisposable> LockAsync()
        {
            var wait = _semaphore.WaitAsync();
            return wait.IsCompleted ?
                        _releaser :
                        wait.ContinueWith((_, state) => (IDisposable)state, 
                            _releaser.Result, CancellationToken.None,
                            TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default);
        }

        public IDisposable Lock()
        {
            _semaphore.Wait();

            return new Releaser(this);
        }

        public bool Wait(int millisecondsTimeout)
        {
            return _semaphore.Wait(millisecondsTimeout);
        }

        public Task<bool> WaitAsync(int millisecondsTimeout)
        {
            return _semaphore.WaitAsync(millisecondsTimeout);
        }

        public void Release()
        {
            _semaphore.Release();
        }

        private sealed class Releaser : IDisposable
        {
            private readonly AsyncLock _toRelease;

            internal Releaser(AsyncLock toRelease)
            {
                _toRelease = toRelease;
            }

            public void Dispose()
            {
                _toRelease.Release();
            }
        }
    }
}
